Two-dimensional tomographic simultaneous multispecies visualization—Part II: Reconstruction accuracy

Recently we demonstrated the simultaneous detection of the chemiluminescence of the radicals OH* (310 nm) and CH* (430 nm), as well as the thermal radiation of soot in laminar and turbulent methane/air diffusion flames. As expected, a strong spatial and temporal coupling of OH* and CH* in laminar and moderate turbulent flames was observed. Taking advantage of this coupling, multispecies tomography enables us to quantify the reconstruction quality completely independent of any phantom studies by simply utilizing the reconstructed distribution of both species. This is especially important in turbulent flames, where it is difficult to separate measurement noise from turbulent fluctuations. It is shown that reconstruction methods based on Tikhonov regularization should be preferred over the widely used algebraic reconstruction technique (ART) and multiplicative algebraic reconstruction techniques (MART), especially for high-speed imaging or generally in the limit of low signal-to-noise ratio

Interface enhancement with textured surfaces in thin-film flows

The interfacial area between the fluid and gas phases plays a significant role in the diffusion and mass transfer-controlled processes. For reactive transport, as in the CO2 absorption in thin-film flows, the time scale of the reaction can be much faster than the time scale of the mass transfer. We, therefore, moot that the absorption rates per volume reactor can be increased if the surface renewal at the interface is enhanced via textured surfaces over which the liquid film flows. The realization of this uncharted potential, however, requires a precise understanding of the complex dynamics between the transient film thicknesses, velocity distributions, and modified surfaces. Hence, we need an accurate and sharp representation of the very thin gas-liquid interface and the ability to capture discontinuities, local penetrations, and the mixing of phases at high temporal and spatial resolutions. In this work, to the best of our knowledge, we investigated for the first time how different surface textures influence the film hydrodynamics and how it is reflected onto the interfacial area statistics at steady conditions using Smoothed Particle Hydrodynamics (SPH). In particular, the effect of structured surfaces on the film hydrodynamics is analyzed statistically for two different texture geometries at two different number densities. In addition, the surface wettability effects are investigated parametrically at three different contact angles. We also analyzed whether texturing help to redistribute the liquid phase to eliminate partial wetting observed in the case of smooth surfaces. Results show that (i) variations in film thickness are strongly influenced by both the presence and number density of textures and (ii) textures can increase the interfacial area by at least six times for the tested cases while alleviating the partial wetting problem. The numerical observations are further confirmed by experimental tests, which also show that with the right blend of geometry, orientation, and density of textures, we can potentially enhance the interfacial area for practical problems such as CO2 absorption